Well tubing rotator and hanger system

ABSTRACT

In one aspect a rotating hanger comprises a dognut sleeve having a bore and an outer profile compatible for support in the casing bowl and sealing thereto and a tubular hanger mandrel fitted rotatably to the dognut sleeve&#39;s bore and having an upper shoulder projecting above the dognut sleeve for interaction with casing bowl holddown screws which, when engaged, restrain rotation and prevent ejection from the casing bowl. In another aspect, an improved well tubing rotator and hanger system is provided the rotatable tubing hanger, a tubular connector sub threaded to the hanger mandrel and a rotator splined to the connector sub, the splined connector sub enabling rotational coupling without imposing hanger loads into the rotator which enables use of smaller, low profile and economical rotators. In another aspect, a rotator having a threaded nozzle wellhead connection is convertible to a flanged rotator.

FIELD OF THE INVENTION

[0001] The present invention relates to apparatus for mounting on a wellhead for hanging and rotating a tubing string in a wellbore.

BACKGROUND OF THE INVENTION

[0002] In a conventional oil well, a reciprocating or rotating string of rods extends from a wellhead and down the bore of well tubing extending downhole to a subterranean pump. Production well fluids are conducted up the tubing. For various reasons, including non-linearity of the well, the rod string and production tubing periodically come into contact and the relative movement therebetween eventually causes wear and even perforation of the tubing with associated loss of production and an expensive maintenance turnover.

[0003] A wellhead typically comprises a wellhead flange and casing bowl secured at the top of a string of casing extending downhole. The casing bowl supports tubing string extending down the casing. The wellhead further comprises means to block the annulus, between the casing and tubing string, and wellhead components secured to the wellhead flange to handle production from the tubing string. The tubing string is usually suspended from a tapered dognut or hanger which is supported in the casing bowl under tubing string weight. In an operating well, the annulus between the casing and the tubing string is usually pressurized and to prevent annulus pressure from lifting and ejecting the tubing string and hanger from the bowl, one or more conventional holddown screws extend radially inwardly from the casing bowl to engage the top of the dognut.

[0004] Various apparatus are mounted on wellheads to allow slow rotation of production tubing so as to distribute wear in the tubing and thus extend the life of the tubing. Two main components enable rotation and are used in a variety of configurations: a rotatable tubing hanger which replaces the conventional dognut, and a low-speed tubing rotator.

[0005] The configuration of the two components has been determined to be very important. Some hangers and rotators are combined into a unitary assembly such as applicant's own U.S. Pat. No. 5,964,286. Others are further integrated into a specialized casing bowl which supports the hanger. One disadvantage with a unitary assembly is that to safely recover the hanger and rotator for maintenance or for use on another well, the well annulus pressure must be equalized before releasing the hanger, usually by killing the well. There are advantages associated with being able to safely remove the rotator such as for servicing, installing other equipment such as a blowout preventor (BOP), or in full well servicing situations to be able to pull the tubing string and rotatable tubing hanger through the installed wellhead components.

[0006] Safety is enhanced if the tubing hanger continues to be restrained to the casing bowl head during servicing so as to avoid a pressure surge and violent ejection of the tubing. Of these two components, the rotator is the most expensive. Accordingly, from an economic aspect, and safe and convenient removal or replacement is desirable.

[0007] Some assemblies separate the bowl and hanger from the more expensive rotator component. These known arrangements are also associated with several disadvantages; typically at least a portion of the weight of the tubing is supported by the rotator, a requirement being that the resulting rotator be robust such as being fitted with thrust bearings capable of supporting tubing loads, and all of which contribute to a large and tall assembly.

[0008] For example in U.S. Pat. No. 5,429,188 to Cameron, a rotator is housed in an assembly which can be removed from the wellhead without affecting the tubing hanger. A two-piece rotating tubing hanger comprises an outer sleeve and an inner mandrel rotatably supported on bearings mounted in the outer sleeve, The tubing string is suspended from the mandrel. The outer sleeve can be secured to the wellhead using the holddown screws however the inner mandrel is not restrained against annulus pressure.

[0009] Similarly, in U.S. Pat. No. 5,465,788 to Wright, a two-piece hanger is fitted to the casing bowl. Tubing is suspended from an inner mandrel which is supported on bearings supported in a outer sleeve secured therein using the bowl's holddown screws. Wright uses an independent tubular rotor shaft extending upwardly from the mandrel and is rotatably secured thereto using splines. A complicated assembly results between the rotator and the tubing hanger in the accommodation of a mandrel retainer, and an insertable key/keyway to prevent rotation and enable threading of pickup tubing. The rotor shaft must be removed before the tubing string can be lifted from the well.

[0010] Even though others have separated the hanger and rotator, applicant is not aware of hanger assemblies in which the components can be safely retained in the casing bowl if the rotator is removed, where the hanger can be readily lifted from the bowl for maintenance, or where the rotator can be easily retrofitted for adding supplemental wellhead components. The present invention provides an improved rotator and an improved hanger which avoid the disadvantages of the prior art.

SUMMARY OF THE INVENTION

[0011] In a preferred aspect of the invention, a rotator and hanger system is provided comprising a two-piece hanger having a dognut sleeve adapted to fit a conventional tapered casing bowl and a hanger mandrel rotatably supported in the dognut sleeve. A string of production tubing is suspended from a lower end of the hanger mandrel and an upwardly projecting shoulder at an upper end of the hanger mandrel can be engaged by the holddown screw for restraining backspin rotation of the tubing or for preventing ejection of the tubing. The system further comprises a low profile rotator mounted to the wellhead flange. An upper mandrel is threaded into the hanger mandrel and extends upwardly to couple the rotator and hanger. The rotator has a bore fitted with a drive collar which is splined to a driven ring gear and splined to the upper mandrel for coupling to hanger while eliminating thrust loads from the tubing. Seals between the rotator bore, the collar and the upper mandrel ensure isolation of the rotator and wellhead from the casing bowl.

[0012] The preferred system is a simplified and inexpensive assembly which permits the rotator to be safely removed or for additional wellhead equipment to be mounted thereto, all without risk of a blowout. The novel tubing hanger enables use of the holddown screws during servicing to prevent rotation of the tubing hanger (for making up threaded joints and for restraining hazardous backspin) and to prevent accidental ejection of the tubing upon removal of the rotator. Supporting the production tubing weight elsewhere enables the manufacture of a very low profile rotator. Further, the use of a upper mandrel which is threaded at it's upper and lower ends results in an inexpensive assembly and enables connection of threaded pulling tools.

[0013] According to one broad aspect of the invention there is provided a novel and safe rotating hanger for suspending a string of tubing from a casing bowl fitted with holddown screws comprising:

[0014] a dognut sleeve having a bore and an outer profile compatible for support in the casing bowl and sealing thereto; and

[0015] a tubular hanger mandrel fitted rotatably to the dognut sleeve's bore and having a lower end from which the tubing string is suspended and an upper end projecting upwardly above the dognut sleeve for forming an upper shoulder so that the holddown screws can be actuated to a first position to engage the hanger mandrel's upper shoulder for restraining rotation and preventing ejection from the casing bowl, and to another position to disengage from the upper shoulder so that hanger mandrel is free to rotate; and to another position to disengage further from the upper shoulder so that the hanger mandrel and dognut sleeve can be removed from casing bowl.

[0016] The hanger mandrel can be locked down using the holddown screws so that the rotator can be removed safely, namely without risk of the hanger backspin, ejection from the casing bowl or leakage.

[0017] Preferably, the tubular hanger mandrel is threaded in its bore at the upper end for connection of threaded pulling tools.

[0018] More preferably, a tubular connector sub is provided comprising an upper mandrel for coupling the rotating tubing hanger and a rotator. This upper mandrel enables rotational coupling without imposing tubing string thrust into the rotator which enables use of smaller and more economical rotators. The upper mandrel is threaded at a lower end to the hanger mandrel and is splined at an upper end for rotational-only coupling with a rotator. If the tubing needs to be removed, a retrieving tool can be threaded to the upper end of the connector sub for lifting the connecting sub, rotatable mandrel and suspended tubing string from the well.

[0019] Further benefits are obtained using a low profile rotator which bears no tubing thrust, isolates the wellhead from the casing bowl, and provides onsite flexibility for various threaded or flanged wellhead configurations. A preferred rotator has a flange housing for mounting to the wellhead flange, said housing having a bore therethrough and a concentric counterbore extending upwardly from a lower mounting face. A concentric drive ring is supported in the counterbore by a retaining ring and is fitted with internal spline for rotational coupling with a collar. The collar is splined inside and out for coupling to the ring gear and to the upper mandrel. A drive gear is fitted to the housing to engage the drive ring. Due to the use of a splined collar to decouple thrust loads, the gear ring need only be lightly supported on bushings. The collar is fitted with seals on its outer surface above and before the ring gear splines to seal to rotator housing. The collar is also fitted with a seal at its inside surface above the upper mandrel splines.

[0020] Accordingly, an improved well tubing rotator and hanger system is provided for a wellhead having a casing bowl, a wellhead flange, and holddown screws. said system comprising a rotatable two-piece tubing hanger having the hanger mandrel which can be engaged and disengaged by the holddown screws, a tubular connector sub threaded to the hanger mandrel and a rotator splined to the connector sub.

[0021] The rotator itself is a unit which is independent of the rotatable hanger. The rotatable hanger supports the loads of the tubing string and the splined connector sub prevents any loads from being transferred to the rotator. As the rotator does not support any tubing loads, it can be very small, required only to provide high-ratio incremental rotation. This rotator can be manufactured with a very low profile, for example as low as 3-¼ inches (8.3 cm), so that the rotator height only adds minimally to the overall wellhead height.

[0022] In preferred embodiments, the tubing rotator is convertible between accepting threaded production tubing to the flow tee or being mountable to a blowout preventor (BOP) when necessary, for example, in the event that the tubing becomes stuck. Such a preferred tubing rotator adaptable to a flange-mounting comprises a housing having an upper surface with threaded nozzle connection for threaded wellhead components and wherein the ring gear, drive gear and collar are located lower than the upper surface so that the threaded connection can be machined off for forming a flange for fifting of flanged components such as a BOP.

[0023] The apparatus and system described above enable a novel method for safely servicing a well's wellhead while avoiding a blowout, the wellhead being fifted with a tubing rotator and a casing bowl fitted with holddown screws, the method comprising:

[0024] providing a two-piece rotating hanger comprising a dognut sleeve having a bore and an outer profile which is compatible for support in the casing bowl and sealing thereto, and a tubular hanger mandrel fifted rotatably to the dognut sleeve's bore, the mandrel having a lower end from which a tubing string is suspended and an upper end projecting upwardly above the dognut sleeve for forming an upper shoulder and connected drivably to the tubing rotator;

[0025] actuating the holddown screws to a first position to engage the hanger mandrel's upper shoulder for safely restraining rotation and preventing ejection of the rotating hanger from the casing bowl; and

[0026] removing the tubing rotator.

[0027] Preferably any stored rotational energy in the tubing string can be relieved by actuating the holddown screws, disengaging from the upper shoulder so that hanger mandrel is free to rotate. Once the well has been hydraulically killed or the annulus has otherwise been rendered safe from differential gas pressure, the rotating hanger and tubing string can be safely retrieved. This can be done with or without the rotator in place. Following the method above, with the rotator removed, the holddown screws are disengaged further from the upper shoulder and so that the hanger mandrel and dognut sleeve can be removed fully from casing bowl.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is cross-sectional view of a hanger and rotator of one embodiment of the present invention;

[0029]FIG. 2 is a cross-sectional view of another embodiment of the invention; and

[0030]FIG. 3 is an exploded cross-sectional view of the embodiment of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0031] Having reference to FIG. 1, a portion of a wellhead 10 is illustrated having a casing bowl 11 secured at the ground surface at the top of casing 12. The casing bowl 11 is a fitting having an upwardly diverging bore 13 for forming the bowl. About the casing bowl 11 is a wellhead flange 14. A rotatable tubing hanger 15 is fitted to the casing bowl 11 and comprises a two-piece assembly of a tubular dognut sleeve 16 and a rotatable hanger mandrel 17. The dognut sleeve 16 has a bore 16 b and an outer profiled surface 18 which is compatible with the casing bowl 11. One or more circumferential seals 19, such as O-rings, seal between the dognut sleeve's outer surface 18 and the bowl 11 and additional circumferential seals 19 b seal between the hanger mandrel dognut sleeve, all of which sealing the well annulus 20 from the wellhead 10. The flange 14 is fitted with a plurality of bolt holes 21 for attachment of various wellhead components (not shown).

[0032] The hanger mandrel 17 has a lower threaded end 30 for connection to, and for suspending, a string of production tubing 31. The hanger mandrel 17 is a tubular member having a bore 17 b therethrough for passing production fluids from the tubing 31 through the tubing hanger 15 to the wellhead 10. At an upper end 32 of the hanger mandrel 17, the bore 17 b is threaded for connection to a variety of components as described later. The hanger mandrel's upper end 32 further comprises a beveled upper shoulder 33 which projects above the dognut sleeve 16 so that it can be engaged by holddown screws 34.

[0033] An upward facing shoulder 35 is formed in the dognut sleeve's bore 16 b for supporting a thrust bearing 36. The hanger mandrel's bore 17 b has a corresponding downward facing shoulder 37 which bears against the thrust bearing 36. An annular groove and snap ring 38 retain the hanger mandrel 17 and dognut sleeve 16 together. Accordingly, the hanger mandrel 17 is rotatable relative to the non-rotating dognut sleeve 16. The holddown screws 34 are adjustable between a first engaged position which engages the hanger mandrel's beveled shoulder and which restrains both rotation of the hanger mandrel and ejection of the production tubing (FIG. 2), a second disengaged position to release the hanger mandrel so as to permit rotation (FIG. 1), and a third fully disengaged position to enable removal of the entire rotating tubing hanger and tubing from the casing bowl 11 (not shown).

[0034] A rotator 40 is adapted for mounting to the wellhead flange 11. The rotator 40 comprises a squat metallic cylindrical housing 41 forming a flange 42 of relatively low height. A ring of bolt holes 43 are positioned about the periphery of the housing 41 which correspond to the wellhead flange 14.

[0035] The rotator 40 has a lower face 44 which is compatible for mounting to the wellhead flange 14 and an upper face 45 having a periphery which is compatible for mounting with other flanged wellhead components such as a BOP. The housing 41 has a bore 46 extending from the lower to the upper faces 44, 45 for conducting fluids from the production tubing 31.

[0036] In the embodiment illustrated in FIG. 1, a threaded nozzle 50 is provided at the upper face 45 for connection of the rotator's bore 46 to wellhead components such as a threaded rod BOP or a flow tee. Further, a gasket 47 is fitted between the lower face 45 and the wellhead flange 14. A fluid passage 48 enables fluid access to the casing bowl 11.

[0037] Best seen in FIG. 3, rotator components are housed within an annular drive cavity or counterbore 60 formed in the housing's bore 46. The counterbore 60 extends upwardly from the lower face 44 and terminates at a top shoulder 61. A ring gear 62 is located concentrically within the counterbore 60. A drive gear such as a worm gear 63 extends transversely through the housing 41 and intercepts the periphery of the counterbore 60 for engaging the ring gear 62 tangentially. The ring gear 62 is aligned with the worm gear 63 and restrained in the counterbore 60 with a lower retainer ring 64 such as a snap ring.

[0038] A connector sub 70 is provided which comprises a tubular upper mandrel 71 which extends between the hanger mandrel 17 and the rotator's ring gear 62. A lower end 72 of the upper mandrel 71 is threaded into the hanger mandrel 17 for co-rotation. Use of threaded connection significantly reduces manufacturing cost. The holddown screws 34 can be actuated to engage the hanger mandrel's beveled upper shoulder 33 for locking its rotation and permitting making up and breaking of the threaded connection 72, 32. The upper shoulder has a profile, beveled is shown, that permits engagement of the holddown screw to both lock rotation relative to the casing bowl and to interfere and prevent lifting or ejection of the hanger mandrel 17 from the casing bowl. If the hanger mandrel 17 is restrained from ejection, so is the dognut sleeve 16 and string of tubing 31.

[0039] A cylindrical collar 80, having inner and outer surfaces 81, 82 fitted with inside splines 81 a and outside splines 82 a respectively, is fitted in an annular space between the ring gear 62 and the connector sub 70 so that rotation of the ring gear 62 drives the collar 80 which drives the upper mandrel 71, hanger mandrel 71 and production tubing 31.

[0040] Typically the production tubing 31 is only rotated at speeds of 1-6 revolutions per day. Accordingly, the ring gear 62 only needs to be supported sufficiently to counter reactive drive forces. The ring gear 62 is sandwiched between thin upper and lower bearing surfaces 83, 84 or bushings contributing to an exceptionally low profile for the flange 42. The lower bearing surface 84 is supported by an annular seal ring 85 which is secured in the counterbore 60 by the retainer 64.

[0041] To facilitate isolation of the casing bowl 11 and the remainder of the wellhead 10, various seals are provided between the rotator 40, the collar 80 and the upper mandrel 71. The annular seal ring 85 is fitted with an inner O-ring seal 90 which seals against a lower depending cylindrical seal surface 81 of the collar 80, and seals with an outer O-ring seal 91 against the bore of the rotator counterbore 60, thereby isolating the rotator components from the casing bowl 11. Similarly, an O-ring seal 92 between an upper cylindrical seal surface 82 of the collar 80 and the upper mandrel 71. Lastly an O-ring seal 93 is provided between the collar 80 and the rotator bore 46 adjacent the upper face 45.

[0042] In another embodiment illustrated in FIG. 2, the upper face of the rotator is flanged, not threaded. The upper face 45 and rotator flange 42 can be manufactured as such or is convertible from the threaded nozzle-fitted rotator of FIG. 1. A conversion is possible by locating the ring gear 62 lower than the upper face 45 so that the threaded nozzle 50 of FIG. 1 can be removed by machining, even while on site, for fitting of a flanged BOP of other flanged component. A gasket groove 95 can be also machined in the upper face. 45

[0043] Referring back to FIG. 1 as demonstrative of rotating operation, the holddown screws 34 are actuated, backing them off slightly to a least a first position to enable the hanger mandrel to rotate. Operation of the worm gear 63 rotates the ring gear 62 and collar 80. The collar 80 drives the upper mandrel 71 which rotates the hanger mandrel 17 and suspended production tubing 31.

[0044] The rotator 40 is removed for servicing, or for access to the production tubing 31. The nature of the worm gear 63 or the high reduction between a drive gear and ring gear 62 usually prevents controlled back-rotation of the production tubing 31. Accordingly, there can be stored rotational energy in the wound up production tubing 31 which can result in a violent backspin upon removal of the rotator 40. The safest approach is to engage the holddown screws and upper shoulder 33, thereby locking the hanger mandrel 17 against backspin rotation before releasing the rotator 40.

[0045] As shown in the exploded view of FIG. 3, once the holddown screws are engaged, the rotator 40 can be safely unbolted from the casing bowl flange 14 and lifted free. The upper mandrel 71 can be left in place or unthreaded for connection of a handling sub or other tool for retrieving the production tubing.

[0046] Should a rotator 40 no longer be required, this expensive piece of hardware can be removed for reuse elsewhere while leaving or abandoning the inexpensive two-piece tubing hanger 15 in place. 

1. A rotating tubing hanger for suspending a string of tubing from a casing bowl fitted with holddown screws comprising: a dognut sleeve having a bore and an outer profile compatible for support by the casing bowl and sealing thereto; and a tubular hanger mandrel fitted rotatably to the dognut sleeve's bore and having a lower end from which the tubing string is suspended and an upper end projecting upwardly above the dognut sleeve for forming an upper shoulder and positioned so that the holddown screws can be actuated to engage the upper shoulder and prevent the hanger mandrel from rotation and ejection from the casing bowl or can be actuated to disengage from the upper shoulder.
 2. The tubing hanger of claim 1 wherein the bore of the dognut sleeve further comprises upward facing shoulder and the hanger mandrel further comprises a outer and downward facing shoulder for rotatable support on the dognut sleeve's upward facing shoulder.
 3. The tubing hanger of claim 2 wherein the hanger mandrel's upper shoulder is positioned so that: the hanger mandrel is locked against rotation and prevented from ejection when engaged by the holddown screws; the hanger mandrel is free for rotation when the holddown screws are disengaged from the upper shoulder; and both hanger mandrel and dognut sleeve are free for removal from the casing bowl when the holddown screws are fully disengaged.
 4. The tubing hanger of claim 3 wherein the hanger mandrel's upper shoulder is beveled so that when the holddown screws are engaged, the upper shoulder is locked against rotation and restrained from ejection from the casing bowl.
 5. The tubing hanger of claim 4 wherein the bore of the upper end of the hanger mandrel is threaded.
 6. A rotator for a coupling with a rotating tubing hanger supported in a casing bowl of a wellhead having a wellhead flange, comprising: a flange housing for mounting to the wellhead flange, said housing having a bore therethrough and a concentric counterbore extending upwardly from a lower mounting face and terminating at a top shoulder; a concentric ring gear supported in the counterbore and sandwiched between the top shoulder and a lower retaining ring, the ring gear having an inner diameter being fitted with internal spline; a drive gear fitted to the flange housing for rotatably driving the ring gear; a concentric and cylindrical collar having an outer surface which is partially fitted with splines compatible with and for rotational coupling with the ring gear, and having an inner surface which is partially fitted with splines for coupling with the rotating tubing hanger.
 7. The rotator of claim 6 further comprising upper and lower annular bushing rings positioned between the top shoulder and ring gear and ring gear and retaining ring respectively.
 8. The rotator of claim 7 further comprising seals between the collar's outer surface and the counterbore below the ring gear the collar's outer surface and the bore above the ring gear the collar inner surface and the rotating tubing hanger above the tubing hanger coupling.
 9. The rotator of claim 6 wherein the flange housing has an upper face and the bore extends into a threaded nozzle.
 10. The rotator of claim 6 wherein the ring gear, drive gear and collar are positioned between the lower and upper faces so that the threaded nozzle can be machined off of the flange housing for converting the upper face to a flanged mounting face.
 11. An improved well tubing rotator and hanger system is provided for a wellhead having a casing bowl, a wellhead flange, and holddown screws actuable to extend into the casing bowl, said system comprising: a rotatable two-piece tubing hanger having a dognut sleeve supported in the casing bowl and having a bore, a tubular hanger mandrel rotatable in the dognut sleeve's bore and having an upper shoulder which, upon actuation of the holddown screws, can be engaged by the holddown screws to lock rotation and disengaged from the holddown screws to permit rotation of the hanger mandrel and to permit removal of the rotating tubing hanger from the casing bowl; a rotator mounted to the wellhead flange; and a tubular connector sub, threaded at a lower end to the rotating hanger and splined at an upper end for rotational-only coupling with the rotator.
 12. The improved system of claim 8 wherein the rotator comprises: a flange housing for mounting to the wellhead flange, said housing having a bore therethrough and a concentric counterbore extending upwardly from a lower mounting face and terminating at a top shoulder; an ring gear retained concentrically within the counterbore, the ring gear being rotatable by a drive gear; and a collar positioned concentric within the counter-bore and being rotatable with the ring gear, and having an interface with the connector sub so as transmit rotation from the ring gear to the connector sub without incurring axial loads.
 13. The improved system of claim 9 wherein the ring gear is sandwiched between the top shoulder and a lower retaining ring has an inner diameter being fitted with internal spline; the drive gear is fitted to the flange housing for rotatably driving the ring gear; the collar has an outer surface which is at least partially fitted with splines compatible with and for rotational coupling with the ring gear, and having an inner surface which is at least partially fitted with splines for coupling with the connector sub.
 14. The improved system of claim 10 further comprising upper and lower annular bushing rings positioned between the top shoulder and ring gear and ring gear and retaining ring respectively.
 15. The improved system of claim 8 further comprising seals between the collar's outer surface and the counterbore below the ring gear the collar's outer surface and the bore above the ring gear the collar inner surface and the rotating tubing hanger above the tubing hanger coupling.
 16. The improved system of claim 8 wherein the hanger mandrel's upper shoulder is positioned so that: the hanger mandrel is engaged by the holddown screws when actuated into the casing bowl so as to lock rotation of the hanger mandrel; the hanger mandrel is free for rotation when the holddown screws are actuated so as to be partially extracted from the casing bowl and are disengaged from the upper shoulder; and both hanger mandrel and dognut sleeve are free for removal from the casing bowl when the holddown screws are fully disengaged.
 17. A method for safely servicing a well's wellhead while avoiding a blowout, the wellhead being fitted with a tubing rotator and a casing bowl fitted with holddown screws, the method comprising: providing a two-piece rotating hanger comprising a dognut sleeve having a bore and an outer profile which is compatible for support in the casing bowl and sealing thereto, and a tubular hanger mandrel fifted rotatably to the dognut sleeve's bore, the mandrel having a lower end from which a tubing string is suspended and an upper end projecting upwardly above the dognut sleeve for forming an upper shoulder and connected drivably to the tubing rotator; actuating the holddown screws to a first position to engage the hanger mandrel's upper shoulder for safely restraining rotation and preventing ejection of the rotating hanger from the casing bowl; and removing the tubing rotator.
 18. The wellhead servicing method of claim 14 further comprising relieving stored rotational energy in the tubing string by actuating the holddown screws to disengage from the upper shoulder and permitting the hanger mandrel to rotate.
 19. The wellhead servicing method of claim 15 wherein once pressure has been reduced below the tubing hanger the method further comprises disengaging the holddown screws from the upper shoulder sufficiently so that the hanger mandrel and dognut sleeve can be removed fully from casing bowl. 